Primary care panel sizes are an important component of primary care practices. Determining the appropriate panel size has implications for patient access, physician workload, and care comprehensiveness and will have an impact on quality of care. An often quoted standard panel size is 2500. However, this number seems to arise in the literature anecdotally, without a basis in research. Subsequently, multiple studies observed that a panel size of 2500 is not feasible because of time constraints and results in incomplete preventive care and health care screening services. In this article we review the origins of a panel size of 2500, review the subsequent work examining this number and effectively debunking it as a feasible panel size, and discuss the importance of primary care physicians setting an appropriate panel size.